Asphalt roofing products are often divided into three broad groups: shingles, roll roofing and underlayment. Shingles and roll roofing typically function as outer roof coverings designed to withstand exposure to weather and the elements. Shingles and roll roofing generally contain the same basic components which provide protection and long term wear associated with asphalt roofing products. These components include a base material made from an organic felt or fiberglass mat which serves as a matrix to support the other components and gives the product the required strength to withstand manufacturing, handling, installation and service in the intended environment. An asphalt coating formulated for the particular service application is often applied to the base material to provide the desired long-term ability to resist weathering and to provide stability under the anticipated temperature extremes. An outer layer of mineral granules is also commonly applied to the asphalt coating to form a surface exposed to the weather which shields the asphalt coating from the sun's rays, adds color to the final product and provides fire resistance.
Typically, shingles are installed on a roof deck such that the shingles are in a row from left to right and the lateral edges of the shingles in the row are contiguous with each other so as to abut each other, i.e. their lateral edges are adjacent to one another. Each row represents a course and the shingles are applied in overlapping courses on the roof deck, wherein the buttlap portion of a subsequent course is placed on the headlap portion of a previous course. The headlap portion of a conventional shingle is at least as wide as the buttlap portion of the shingle so that when the shingles are installed on a roof deck in overlapping courses, the entire buttlap portion of a subsequent course has headlap beneath it. This manner of installation prevents leakage to the roof deck where the lateral edges of the shingles abut each other.
In a typical roofing system, contiguous shingles in a row abut each other at their lateral edges. Thus, when the shingles are exposed to wet weather, it is possible that leakage can occur at the region where the shingles abut. To prevent that, overlapping subsequent rows of shingles are installed in an offset pattern and each shingle's headlap portion is at least as wide as the buttlap portion. Thus, when the shingles are applied to the roof in a plurality of courses and the buttlap portion of a second course of shingles is laid over the headlap portion of a first row of shingles there is always headlap present underneath the regions where the contiguous shingles in a row abut. Any water penetrating the places where lateral edges of shingles abut contacts the headlap rather than the roof deck.
In certain instances, for aesthetic purposes, shingles have been applied to a roof deck such that the lateral edges of neighboring shingles overlap. U.S. Pat. No. 2,687,701 describes single layer tabbed asbestos cement roofing shingles comprising varying length tabs. When the shingles are applied to a roof deck, their lateral edges overlap. The shingles comprise tabs which extend above and over the buttlap portion of a previous course when a subsequent course is installed. The overlapping and varied lengths of tabs are intended to create a more dimensional appearance.
U.S. Pat. No. 3,919,823 describes single layer asphalt roofing shingles. The shingles are not tabbed but instead comprise various projections. The shingles are installed such that their lateral edges overlap to create what is described as a “shadow effect” which will vary depending on the time of day.
U.S. Pat. Nos. 4,333,279 and 4,527,374 describe strip or tabbed single layer asphalt shingles. The shingles comprise various edges at least one of which is an alignment edge. The shingles are overlapped using the alignment edge in order to achieve a desired pattern when the shingles are installed on a roof deck.
U.S. Pat. No. 6,990,779 describes a laminated roofing shingle system including a reduced-width headlap portion and an interply material that is installed under the buttlap portion in order to compensate for the reduced-width headlap portion and provide protection to the roof deck.
U.S. Patent Application Publication 2004/0182032 describes a multi-layer laminate shingle with a reduced-width headlap portion. The shingle has a base layer and at least a second layer above the base layer. At one end of the shingle the base layer projects beyond the second layer while at the other end the second layer projects beyond the base layer. When the shingles are laid in a course along the roof, the projecting end of the second layer overlaps the projecting end of the base layer of the next shingle, forming a shiplap joint over all or substantially all of the width of the shingle.
Each of the above-referenced patents is incorporated herein by reference for all purposes within this application.